in this video we're going to learn about separating mixtures So we'll cover how filtration can separate insoluble solids from liquids and how evaporation and crystallization can separate soluble solids from liquids Before we start though I want to point out some key terminology First as this video is all about separating mixtures a mixture is defined as two or more different types of substances that are mixed together in the same place And importantly that aren't chemically joined Some mixtures are formed when we mix together an insoluble solid which means it can't dissolve and a liquid In this case the solid doesn't dissolve It just sinks to the bottom of the liquid Like when we mix sand with water Another common type of mixture are solutions which are formed when one substance the solute dissolves in another substance the solvent A classic example of this is the soluble solid salt dissolving in water to form salt water In this case the salt is the solute the water is the solvent and the salt water is the solution As the different substances in mixtures aren't chemically joined we can separate them using a few different physical techniques Which technique we use depends on whether we're separating insoluble solids from liquids or soluble solids from solutions The first and simplest technique that we're going to look at is filtration which separates insoluble solids from liquids This is basically the same process as using a civ to separate food from water when you're cooking But in chemistry we normally use filter paper which has lots of tiny holes in it that are small enough so that water can pass through but not solids We often place the filter paper within a filter funnel as well so that we can easily pour our mixture through it leaving the solid behind on the paper Now if we instead have a solution so where a soluble solid has dissolved in a liquid then this time we won't be able to filter it out In this case we'll have two options evaporation or crystallization For evaporation we place our solution in an evaporating dish or a crucible which we normally place on a tripod and then slowly heat it with a Bunson burner This will cause the solvent to start evaporating and the remaining solution to get more concentrated After a while crystals will start to form because it's so concentrated and eventually all of the solvent will disappear leaving us with dry crystals of our solid Now the benefit of this evaporation technique is that it's a relatively quick and easy way to separate a soluble solid from a solution The issue though is that some solids will decompose when they're heated which we call thermal decomposition So even though we could use this technique to isolate the solid we'd end up breaking it down into something else This means that for solids that are susceptible to thermal decomposition we have to use a slightly slower technique called crystallization The first step of this method is still to place our solution into an evaporating dish and heat it But this time we need to heat it more gently So we might use a water bath instead of a Bunson burner Then once some of the solvent has evaporated and we start to see crystals forming in the solution we stop heating it and leave it to cool As the solution cools more and more crystals will form because solids are less soluble at colder temperatures The next thing we'd have to do is filter out these crystals from the remaining solution using filter paper and a funnel And then the last step would be to dry our crystals by either leaving them somewhere warm or warming them up in a drying oven If you haven't heard yet you can find all of our videos on our website cognito.org You'll also find questions flashcards exam style questions and pass papers And we track all of your progress so that you always know what to study next So sign up for free by clicking here or browse our playlist here on YouTube